I've had a practice on a random screen from my local scrappy, and the corners are easy to do, using a template to cut around each side (a coke can in this case), and then crushing the glass after jiggling it first with a pair of pliers and then cutting the laminate off with a stanley blade.
I'll be doing this to my build and getting some screen rubber/trim from Woolies, which is just up the road from me.
The screen at the bottom is not advisable to cut as this is where the scuttle bonds too apparently.